Tim O’Brien and Darrell Scott first met on a publisher’s songwriting appointment, but their musical careers have since intersected in many more organic circumstances. Their second collaboration (the first was 2000’s Real Time) finds them playing together as a live duo at the Grey Eagle in Asheville, N.C. Recorded in 2005 and 2006, the set list includes original songs (including Scott’s “Long Time Gone,” which was a hit for the Dixie Chicks) and covers of titles by Hank Williams (“House of Gold,” sung a cappella), Townes Van Zandt (“White Freightliner Blues”), Gordon Lightfoot (“Early Morning Rain”), Keith Whitley (“You Don’t Have to Move That Mountain”) and Lefty Frizzell (“Mom and Dad’s Waltz”). What makes these performances truly exciting is the unrehearsed vitality of players sharing a country music heritage and the improvisational skills of masters. The performances are fresh and surprising not just to the audience, but to the pair themselves as they build harmonies and fuel the songs with guitar and mandolin. Given how artfully the two intertwine and play off one other, it’s hard to imagine they could really be much better than this.